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R. S. WILBUR AND W. H. BENDERNAGEL.

TELEPHONE SYSTEM.

APPLICATION HLED DEC 28. ms.

1,371,717. Patented Mar. 15,1921.

/n ve M f0 K6 Ray 6. Wf/bu/ I/V/W/am /7.Be/7demaqe/ UNITED STATES PATENT OFFICE.

RAY S. WILBUR, OF LYNDHURST. NEW JERSEY, AND WILLIAM H. BENDERNAGEL, O1!

BROOKLYN, NEW YORK, ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCORPO- RATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

' TELEPHONE SYSTEM.

Specification of Letters Patent.

Patented Mar. 15, 1921.

Application filed December 28, 1918. Serial No. 268,742.

To all whom it may concern: 7

Be it known that we, RAY S. WILBUR and VVILLIAM H. BENDERNAGEL, citizens of the United States, residing at Lyndhurst, 1n the county of Bergen, State of New Jersey, and at Brookl n, in the county of Kings, State of New ork, respectivelv, have invented certain new and useful mprovements in Tele hone Systems, of which the following is a fiill, clear, concise, and exact description.

This invention relates to telephone systems and more particularly to a system designed for the efficient transmission of currents of frequencies within a desired range, and the primary object thereof is to so organize such a system that it will also be highly efiicient in the transmission of currents of frequencies outside the desired range. Such a system may comprise a transmission line over which is transmitted both telephonic and signaling currents, the line being designed primarily for the efficient transmission of currents within the telephonic range, but normally relatively ineflicient in the transmission of signaling currents of much lower frequencies.

If two sections of a transmission line hav ing different impedances or two transmission lines of different impedances are joined, provision is usually made for preventing undue losses resulting from the transmission of telephonic currents from a line of one im-- edance to a line of another impedance.

hese losses are frequently termed refiection losses and to reduce such losses, the lines or sections of the line are frequently joined through an auto-transformer. These auto-transformers, while of low impedance to currents having frequencies within the voice or telephonic range, are of high impedance to currents of lower frequencies, such as are employed for controlling signals.

Voice or telephonic currents vary in frequency over a considerable range and in the propagation of such currents over a transmission line those voice currents of the higher frequencies are attenuated much more rapidly than those of the lower frequencies. If such voice currents with the higher frequency greatly attenuated in comparison to the lower frequencies are amplified when in this condition, there is a cumulative effect in this difference in attentuation in the amplified currents. On long transmission lines equipped with a number of amplifying devices, this diiference in attenuation of the higher and lower frequency voice currents accumulates to such an extent that there is such serious distortion in the currents received at the distant end of the line as to seriously impair the quality of the speech re ceived. In order that this distortion ma be eliminated, it has been proposed to inc ude in the transmission line an impedance arrangement having characteristics such thatit attenuates currents of lower frequencies much more rapidly than those of higher frequencies, thereby permitting the transmission of telephonic currents of all frequencies with practically uniform attenuation. These impedance arrangements, which are known as attenuation equalizers, are described in an application of Ray S. Hoyt, Serial No. 242,567, filed June 29, 1918.

Furthermore, in order that a high degree of efficiency may be attained in the transmission of voice currents over a transmission line, it has been found desirable to regulate the gain or amplification of the repeaters or amplifiers, and in order that this may be accomplished there is associated with the input of each amplifier a potentiometer which controls the input current of the amplifier.

All apparatus, such as auto-transformers or other devices for minimizing reflection losses, attenuation equalizers for preventing distortion, and potentiometers for controlling the gain or amplification of amplifiers, as well as the amplifiers connected with transmssion lines, being designed with par ticular reference to the efficient transmission of currents of voice or telephonic frequency, a transmission line so equipped is relatively inefficient in the transmisson of currents of frequencies outside of the voice or talking range. For example, a line so equipped is relatively ineflicient for the transmission of ringing or signaling currents for controlling the operation of signals. Such signaling or ringing currents are usually of a frequency well below those encountered in the range of voice currents. Where, therefore. it is desired to transmit such signaling or ringing currents over transmission lines which may be e uipped with amplifiers designed for the e cient transmission of voice currents and to employ the same amplifiers Another object of this invention is to provide a system comprising transmission lines of different impedance over which, when joined, both talking and signaling currents may be efficiently transmitted. V

In attaining the objects of this invention, there is associated with each amplifying station on a transmission line an electrorespoir sive device, responsive to ringing or signaling currents, but non-responsive to telephonic or voice currents. This ringing responsive device, when responding, controls through certain switching devices the autotransformer, attenuation equalizer and potentiometers, whereby the normal condition of these devices is altered in such a manner that the line is transformed temporarily,

from one highly efiicient for the transmission of voice or telephonic currents to one highly efiicient for the transmission of ringinglor signaling currents.

ore particularly stated, ringing re sponse device s an electromagnetic relay which, when operated, controls switching relays, one of which opens up the shunt por- 7 tion of the auto-transformer, which joins two line sections of different impedance, thereby increasing the efiiciency of the line in the transmission of ringing currents. A condenser of high impedance to signaling currents is substituted for the shunt portion of the auto-transformer and cooperates with the primary winding of a'repeating coil to form a closed resonating circuit at the sig naling current frequency,"thereby greatly increasing the elficiency of the line in the transmission of signaling currents. An other of the switching relays disconnects the attenuation equalizer from the line, thereby preventing an undue attenuation of the ringing currents, and alters the setting of the potentiometers to increase the amplification of the amplifiers.

For a more complete understanding of this inventionreference should be had to the following description considered in connec-' tion with theaccompanying drawing illustrating one embodiment of the invention.

Referring to the drawings, L represents 1 a section of thetransmission line of one impedance, which is joinedthrough an autotransformer 5 with another section L of the transmission line of a differentimpedance. Section L which includes a transformer or and an output coil 10. Included in series with the secondary winding of the repeating coil 6 is an attenuation equalizer 11 of the parallel type comprising a resistance 12 connected in parallel with a condenser'1-3 and a retardation coil 1 1. Between the secondary winding of the repeating coil 6 and the primary winding of the inputcoil 7, there is connected a potentiometer 15, which controls the gain or amplification of the amplifier 8. A potentiometer 16 is associated vwith the input circuit of the amplifier 9 for controlling the gain or amplification thereof. In the output circuit of the amplifier 9, there is connected a ringing response relay 20 which, through a transfer relay 21, controls two switching relays 22 and 23. Switching relay 22 controls the opening up of the shunt portion of the auto-transformer '5 thereby disconnecting the auto-transformer from the line sections, and substituting the condenser 25 in a bridge of the line section. Switching relay 23 controls the short-circuiting of the attenuation equalizer 11, the opening up of the shunt of the potentiometer l5 andthe ings of the repeating coil 6, and is repro- 5 duced' by induction in the secondary windings of this repeating coil 6. This repro-' duced ringing current thereupon traverses the circuit including the attenuation equalizer 11, the potentiometer 15 and the primary winding of the input coil 7. These currents are then transmitted in succession through the amplifiers 8 and 9 and are amplified, so that upon reaching the output circuit of the amplifier 9 they energize the ringing response relay 20. Theinclusion of the auto-transformer 5 and the attenuation equalizer 11 in the line, and normal settings of the potentiometers 15 and 16, serve to cause quite serious attenuation of the ringing currents, but sufficient current reaches the relay 20 to cause the operation thereof. The relay 20, while preferably connected in the output circuit of the second amplifier to take advantage of the amplification of the greatly attenuated initial signaling currents, may, of course, if desired, be connected in any other portion of the line. Upon the op eration of this relay 20, transfer relay 21 releases, causing the energization of switching relays 22 and 23 over a circuit from battery through the windings of these two relays in parallel and the contact of the relay 21 to ground. Switching relay 22 opens its normal and closes its alternate contact. The opening of the normal contact opens up the two middle or shunt windings of the autotransformer 5, disconnecting the auto-transformer from the line and substitutes a condenser 25 for the shunt portion. This condenser. which is of high impedance to ringing currents, is of such capacity as to form with the primary windings of the repeating coil 6, a closed resonating circuit in which circulate local oscillatory currents which attain a maximum at the ringing frequency of 133 cycles. These currents traversing the primary winding of the repeating coil 6 induce currents into the secondary winding thereof, which are transmitted through the input coil into the amplifiers. The shunt path, which includes the condenser 25, therefore presents a very high effective resistance to ringing currents, whereas with the two middle windings of the transformer 5, connected in bridge of the line sections, a low effective resistance is presented to currents of this frequency.

The switching relay 23 in operating closes its contact 26, thereby establishing a shortcircuit about the attenuation equalizer 11, which effectively removes this equalizer from the circuit. By the substitution of the low resistance path through the contact 26 of relay 23 for the attenuation equalizer 11. the input circuit is rendered of much lower impedance to the ringing currents. This substitute path transmits lower frequency currents with less attenuation than higher frequency currents, and therefore is much to be preferred for the transmission of signalin currents.

e opening of contact 27 of switching relay 23 opens up the shunt path of the potentiometer 15, thereby increasing the gain of the amplifier 8 at the frequency of the ringing currents. The opening of contact 28 and the closing of contact 29 of switching relay 23 changes the setting of the potentiometer 16 in such a manner that a greater amount of current is transmitted to the am plifier 9, whereby the gain thereof, at the Wency of ringing currents is increased.

at is claimed is:

1. In a transmission system, in combination, a transmission line over which currents of higher frequencies are transmitted with greater attenuation than currents of lower frequencies, means associated with the transmission line for equalizing the attenuation thereof, so that currents of all frequencies within a desired range are transmitted with practically uniform attenuation, and means for rendering the attenuation equalizing means ineffective when currents of frequencies outside the desired range are transmitted over the line.

2. In a transmission system, in combination, a transmission line over which currents of higher frequencies are transmitted with greater attenuation than currents of lower frequencies, means associated with the transmission line for equalizing the attenuation thereof, so that all frequencies within a desired range are transmitted with practically uniform attenuation, and an electroresponsive device responsive to currents of frequencies outside the desired range for rendering the attenuation equalizing means ineffective to currents of such frequencies.

3. In a transmission system. in combination, a transmission line over which currents of higher frequencies are transmitted with greater attenuation than currents of lower frequencies, means associated with the transmission line for equalizing the attenuation thereof, so that all frequencies within a desired range are transmitted with practically uniform attenuation, an auxiliary path over which currents of lower frequencies are transmitted with less attenuation than currents of higher frequencies, and means responsive to currents of frequencies lower than those within the desired range for substituting the auxiliary path for the attenuation equalizing means.

4. In a transmission system, in combina tion, a transmission line over which telephonic and signaling currents are transmitted with greater attenuation of the higher frequency currents than the lower frequency currents, means associated with the line for equalizing the attenuation thereof, so that telephonic currcnt-s of all frequencies are transmitted with practically uniform attenuation, and an electromagnetic relay responsive to signaling currents for rendering the attenuation equalizing means ineffective to such signaling currents.

5. In a transmission system, in combination, a transmission line over which telephonic and signaling currents are transmitted with greater attenuation of the higher frequency currents than the lower frequency currents, means associated with the line for e ualizing the attenuation thereof, so that tglephonic currents of all frequencies are tranmitted with practically uniform attenuation, amplifying means associated with the transmission line for amplifying both telephonic and signaling currents, and means responsive to signaling currents for rendering the attenuation equalizing means ineffective to such signaling currents.

6. In a transmission system, in combination, a transmission line over which telephonic and signaling currents are transmitted with greater attenuation of the higher frequency currents than the lower frequency currents, means associated with the line for equalizing the attenuation thereof, so'that telephonic currents of all frequencies are transmitted with practically llllllfOlIIl attenuation, amplifying means associated with the transmission line for amplifying both telephonic and signaling currents, means for determining the amplification of the amphfier, and means responsive to signaling currents transmitted over the line for rendering the attenuation equalizing means ineffective and for controlling the amplification determining means.

7. A transmission system comprising two line sections over which telephonic and signaling currents are transmitted, means connecting the line sections for minimizing reflection losses resulting from the transmission of telephonic currents from one line section to the other, and means responsive to signaling currents transmitted over one line section for rendering the reflection loss minimizing means ineffective to such signaling currents, thereby increasing the efficiency of the line when signaling currents are transmitted.

8. In a transmission system, incon1bination, two line sections over which telephonic and signaling currents are transmitted, a transformer connecting the line sections for minimizing reflection losses resulting from the transmission of telephonic currents from one section to the other and an electro-responsive device responsive to signaling currents for disconnecting the reflection loss minimizing means from the line sections.

9. In a transmission system, in combination, two line sections over which telephonic and signaling currents are transmitted, an impedance connected with the second line section, a transformer connecting the two line sections for minimizing reflection losses resulting from the transmission of telephonic currents from one line section to the other, means responsive to signaling current for disconnecting a portion of the transformer from the line sections, and a condenser connected in circuit with the impedance upon the response of said means for increasing the efficiency of the line to signaling currents. i V

10. In a transmission system, in combination, two line sections over which telephonic and signaling currents are transmitted, an

auto transformer connecting the line sections for minimizing reflection losses resulting from the transmission of telephonic currents from one line section to the other, a repeating coil connected in the second line section, a relay responsive'to signaling currents for disconnecting the shunt portion of the auto-transformer from the line sections, and a condenser substituted. for the shunt tion, a transmission line, a two-stage ampli fier set included in the line for amplifying both talking and ringing currents and com prising a first amplifier whose output circuit isconnected with the input circuit of a second amplifier, a potentiometer connected with the input circuit of the second amplifier for controlling the amplification thereof, and means for controlling the potentiometer when ringing current is transmitted over the line to increase the amplification of the second amplifier.

12. In a transmission system, in combination, a transmission line, a two-stage amplifierset included in the line for amplifying both talking and ringing currents and com prising a first amplifier whose output circuit is connected with the input circuit of a second amplifier, a potentiometer associated with the input circuit of each amplifierfor controlling the amplification thereof, and means for opening up the shunt of the first potentiometer and for alteringthe second when ringing current is transmitted over the line to increase the amplification of both amplifiers. 7

13. In a transmission system, in combination, a transmission line, a twostage amplifier set included in the line for amplifying both talking and ringing currentsand comprising a first amplifier whose output circuit is connected with the input circuit of a second amplifier, a potentiometer associated with the input circuit of the second amplifier for controlling the amplification thereof, and an electromagnetic relay responsive to amplified ringing current for controlling the potentiometer to increase the amplification of the second amplifier. 7

14. In a transmission system, in combination, a transmission line over which telephonic and signaling currents are transmitted with greater attenuation ofthe higher than the lower frequency currents, means associated with the line for equalizing the attenuation thereof so that telephonic currents of all frequencies are transmitted with practically uniform attenuation, an amplifier included in the line for amplifying the attenuated telephonic and signaling currents, and an electromagnetic relay respon sive to amplified signaling currents for interrupting the operative association of the attenuation equalizing means with the line to decrease the attenuationof the signaling currents.

15. In a transmission system, in comhination, a transmission line over which telephonic and slgnalingcurrents are transmltted w th greater attenuation of the h gher than the lower fre uency currents, means associated with the ine for equalizing the attenuation thereof so that telephonic currents of all frequencies are transmitted with practicall uniform attenuation, an amplifier inclu ed in the line for amplifying the attenuated telephonic and signaling currents, a potentiometer controlling the amplification of the amplifier, an electromagnetic relay responsive to amplified signaling currents, an a switching relay operating upon the response of the electromagnetic relay for interrupting the operative association of the attenuation equalizing means with the line to decrease the attenuation of the signaling currents and for altering the setting of the potentiometer to increase the amplification of the amplifier.

16. Atransmission system comprisin two sections of a transmission line of difl erent impedance over which high and low frequency currents are transmitted, means join ing the line sections for minimizing reflection losses resulting from the transmission of high frequency currents from one line sec tion to the other, and means responsive to low frequency currents for rendering the reflection loss minimizing means ineffective to such low frequency currents.

naling currents are transmitted, means joining the line sections for minimizing reflection losses resulting from the transmission of telephonic currents from one line section to the other, an amplifier for amplifying signaling currents transmitted over one line section, and an electromagnetic relay responsive to amplified signaling currents for controlling the reflection loss minimizing means.

18. Atransmission system comprisin two sections of a transmission line of di erent impedance over which telephonic and signalin currents are transmitted, means joining the line sections for minimizing reflection losses resulting from the transmission of telephonic currents from one line section to the other, and an electromagnetic relay responsive to signaling currents transmitted over one line section or controlling the reflection loss minimizing means.

In witness whereof we hereunto subscribe our names this 23rd day of December, A. D. 1918.

RAY S. WILBUR. WILLIAM H. BENDERNAGEL. 

